<!DOCTYPE html>

<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title></title>
        <meta name="description" content="">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link rel="stylesheet" href="">
    </head>
    <body>
      
        <script>
      function fn(name ,age){
        name=name ||"tom";
        age=gae|| 17;
        console.log(name+","+age);
      }
      function fn2(name,age){
        name=(typeof name!='undefinded' ? name:'tom');
        name=(typeof age!="undefined"?age:17);
        console.log(name+","+age);
      }
      function fn3(name='tom',age=17){
        consoel.log(name+","+age);
      }      
      fn();
      fn2();
      fn3();
      </script>
    </body>
</html>